The present invention relates to a video disk apparatus for writing/reading digital continuous data and specifically, digital video data and, more particularly, to a disk apparatus having the function of time-divisionally and alternately writing and reading digital video images on a plurality of channels.
A video disk apparatus for writing/reading digital video data on/from a storage medium such as an optical disk by using a digital video compression technique represented by MPEG is under development.
According to a conventional video disk apparatus using an optical disk, the digital video data compressed by an MPEG encoder serving as a digital video compressor or digital video data transmitted from a broadcast station, a CATV (cable TV), or the like is temporarily stored in a buffer memory at a predetermined bit rate. This buffer memory is used for adjusting the difference between the bit rate of input digital video data (the number of bits transmitted per second) and the write/read speed of an optical disk (the number of bits which can be written/read per second). In general, the bit rate of input digital video data is lower than the write/read speed of the optical disk.
Digital video data is written in the optical disk as follows. The digital video data is read out from the buffer memory at the write speed of the optical disk first. The data is then modulated into a signal suited for a write by a modulator/demodulator section. The signal is input to the optical head. The digital video data is written in the optical disk by this optical head.
Digital video data is read from the optical disk as follows. The optical head is moved to a radial position, on the optical disk, in which the digital video data of a desired video image is written. The digital video data is then read from the optical disk by the optical head. The read digital video data undergoes demodulation which is a reverse process to that in the write operation. The resultant data is input to the buffer memory. The data is sent from this buffer memory to an MPEG decoder serving as a digital video decompressor at the bit rate of the digital video data to be decompressed. The decompressed video data is input to a monitor to be displayed as a video image.
As, for example, the number of channels to be distributed increases, demands have arisen for the use of such a video disk apparatus, as one of usage patterns, in writing video images on a plurality of channels in the same time zone. The above conventional video disk apparatus, however, can write only one-channel digital video data at once. To write digital video data on a plurality of channels at once, a plurality of video disk apparatuses must be prepared. As a result, the user must bear a high cost and ensure an installation space.
Analog video recording/reproduction apparatuses capable of writing two-channel video images at once are commercially available. In such a conventional analog video recording/reproduction apparatus, however, the recording band per video image must be reduced, and hence a deterioration in image quality is inevitable.
As described above, according to the conventional techniques, a plurality of video disk apparatuses must be prepared to write video,images on a plurality of. channels in the same time zone. As a result, the user must bear a high cost and ensure a large installation space. When two-channel video images are to be written at once by an analog video recording/reproduction apparatus, since the recording band per video image is reduced, the image quality deteriorates.